1. Field of the Invention
The present invention relates to switches for electromagnetic waves and, more particularly, to RF switches which may be controlled electronically.
2. Description of the Prior Art
In many fields of electronics, it is often necessary to switch the signal from one circuit to another. Commercial semiconductor and ferrite type switches are available.
Ferroelectric materials have a number of attractive properties. Ferroelectrics can handle high peak power. The average power handling capacity is governed by the dielectric loss of the material. They have low switching time (such as 100 nS). Some ferroelectrics have low losses. The permittivity of ferroelectrics is generally large, as such the device is small in size. The ferroelectrics are operated in the paraelectric phase i.e. slightly above the Curie temperature. The ferroelectric switches can be made of thin films, and can be integrated with other microwave/RF devices. Inherently, they have a broad bandwidth. They have no low frequency limitation as in the case of ferrite switches. The high frequency operation is governed by the relaxation frequency, such as 95 GHz for strontium titanate, of the ferroelectric material. The loss of the switch is low with ferroelectric materials with a low loss tangent. A number of ferroelectric materials are not subject to burnout.
A multi-stub transmission-reflection type ferroelectric switch has been studied (1). The optical deflection and modulation by a ferroelectric device has been studied (2,3). A liquid ferroelectric optical switch has been reported (4). A patent was issued on an RF phase shifter (5).
No publication has so far been made on ferroelectric type RF total internal reflection. There are significant differences between the RF and optical deflectors. In the optical deflector, the light ray travels through a very small portion of the active medium. In the RF switch, the RF energy will travel through the entire portion of the active medium. The wavelength of RF is several orders of magnitudes greater than the optical wavelengths.
The dimensions of the optical deflector are many times the optical wavelengths. The optical beam diameter is many times the optical wavelength. The width of the switch is generally a fraction of the RF wavelength. The biasing circuit, for the optical deflector, is far away from the optical beam. The biasing circuit, in the case of the RF switch, has to be isolated, by design, from the RF circuit. The biasing field, in the case of optical deflector, can be parallel or perpendicular to the direction of the electrical field of the optical beam. For the RF switch, the direction of the biasing field is parallel to the direction of the electrical field of the RF beam. After deflection, the optical beam travels a medium of same impedance as the incident beam.
The ferroelectric rf switch provides a third alternative to the semiconductor and ferrite switches. Depending on a trade-off studies in individual cases, the best type of switch can be selected.